Method of making vibratory devices



March 20, 1934. w. s. KELLAR 1,951,873 METHOD OF MAKING VIBRATORY DEVICES I Filed Jan. 15, 1931 Patented Mar. 20, 1934 Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application January 013,

' Claims,

This invention relates to vibratory devices and methods of producing the same, and more particularly to diaphragms and other vibrating devices formed of aluminum alloys, and to methods of producing such devices.

The object of the invention is to provide an improved and efiicient method of producing metallic vibratory devices.

The invention is particularly applicable to the production of diaphragms and other vibratory parts used in the transmission, recording and reproduction of sound, examples of such rts being microphone diaphragms and light gve ribbons for sound recording apparatus. S ch a vibratory part is usually maintained for considerable periods of time under such tension that its natural period of vibration is above the usual, range of the ordinary human voice, and this requires special qualities of lightness, tensile o strength, and resistance to fatigue in the metal from which the part is made. By proper selection of the alloy from which such parts are made, as well as by special steps in the treatment and forming of the alloy, the present invention aims to produce parts which will meet these and other requirements.

. In one embodiment, wherein the invention is applied to the production of a microphone diaphragm, the metal from which the diaphragm is to be made consists of an aluminum alloy which is formed into a strip and then heat-treated and quenched, after which it is rolled to the desired thickness and seasoned at about 212 F. to increase its toughness, and resistance to fatigue.

85 From this strip the diaphragmsor other parts are then-formed. 4 Y

The invention will be more fully understood from the following description, taken in connection with the appended drawing,-in which v Fig. 1 is a sectional view of a microphone comprising a diaphragm which may be formed in ac-- cordance with the invention;

Fig. 2 is a sectional view of a sound recording device comprising a vibratory ribbon which may Fig. 3 is a fragmentary. sectional view' taken on the line 3-3 of Fig. 2. v v

The preferred composition of the alloy from which the vibratory parts are made is as follows: 1

50 Copper 3.15% to 4.50%

.20% to .50%. .40% t0 1.00%j

Silicon Magnesium Manganese be formed in accordance with the invention, and

40% tol.00%f" Iron Not more than .50 65 Aluminum Balan e? 1931, Serial No. 508,483.

This alloy is first reduced to the form of a strip about 3" wide and .020" thick and having a mirror finish. The strip is then heat-treated by maintaining it at a temperature of 930? to 960 F. for 30 to minutes. At the completion of the heat-treatment the strip is quickly quenched inoil or other quenching liquid, after which it will be found to have'a tensile strength of about 55,000 pounds per square inch. The strip is then cold-rolled to a thickness of about .0017", pref-' erably by the method and apparatus disclosed in W. S. Kellar Patent 1,655,373 dated January 3, 1928, wherein the strip is given several passes for each setting of the rolls. produce a mirror polish on the diaphragms, the rolls used in this operation may be provided with a mirror polish, and the surface of the strip may be polished continuously, as by bulling during the rolling operation in order to preserve the mirror finish with which it is provided at the beginning of the rolling operation.

The strip, having been rolled to the desired thickness,.is then seasoned by maintaining it at a temperature of about 212' F. for about 40 hours to relieve internal stresses and increase If .it is desired to ,v

its tensile strength andresistance to fatigue.

The tensile strength of the seasoned strip will be about 75,000 pounds per square inch. The diaphragms are then formed from the strip by punching or otherwise, afterwhich they are provided with electrodes, preferably by the. cathode sputtering method disclosed in H. F. Fruth Patent 1,765,413 dated June 24, 1930. The diaphragms are then :assembled in microphone frames and stretched to raise their frequency of vibration to the desired value.

.Fig. 1 illustrates the relation of the diaphragm to the microphone, the reference numeral 10 designating a circular diaphragm having its edges held under pressure between annular compression blocks 12 and 14, rings 16 and 17 of emery ,cloth or similar frictional material being interposed between the diaphragm and the compressionblocksto-prevent slipping. An annular anvil 20 is mounted within the block 12 and is provided with a smooth rounded surface which'engages the diaphragm to permit a slight'sliding action with a minimum of friction. The dia-' phragm is put under the desired tension by means of a collar 22 having threaded engagement 'with the block 14 and adapted to engage the diaphragm inwardly of the anvil 20 tostretch it until the desired frequency of vibration is obtained. In the case of a microphone wherein the portion of the diaphragm which is free to vibrate measures ico - in connection with Fig. l.

1% inches in diameter, the natural frequency may be about 5700 cycles per second.

, As illustrating a further use of the invention, Figs. 2 and 3 show a light valve for a sound recording apparatus wherein a ribbon 24 is doubled upon itself to allow two of its passes to lie adjacent a slit 26 formed in an anvil 27, thereby to control the passage of a beam of light projected from a. source of light (not shown) through the slit to a moving sensitized film (not shown) positioned below the anvil 27. The ends of the ribbon are secured to pins 28 and the ribbon is looped over a button 30 which is secured by means of a spring 32 to a post 34 to maintain the ribbon under predetermined tension.

The ribbon shown in Figs. 2 and 3 is formed from a strip of aluminum alloy similar to that described above in connection with Fig. 1, the strip being cold-rolled from a thickness of about .020" to about .010" and then heat-treated and quenched in a manner similar to that described After being heattreated and quenched the strip is further re- .duced by cold-rolling to a thickness of- .0005" and is then seasoned by maintaining it at a temperature of about 212 F. for about 40 hours, after which it is slitted into ribbons such as that shown in Figs. 2 and 3, the dimensions being about .0005" x .006" x 12". The ribbon should be capable of sustaining a tension corresponding to a frequency of about 9000 cycles per second in a length of about inch without breaking, and

this requiresa tensile strength in the neighborhood of 75,000 pounds persquare inch, which is readily obtained by the above described process.

The invention is also capable of use in connection withthe production of diaphragms or membranes designed to respond to pressure fluctuations in pressure reducing valves and similar apparatus where lightness, strength, and sensi tivity to variations in pressure are desired. Such diaphragms or membranes are not usually free to vibrate in the same manner as are the devices above described, but are designed to be moved out of a normal position by exterior forces and to be restored in such normal position by the elasticity of the material, and are therefore intended to be included within the term vibratory devices as it is used in this application. The term aluminum base alloy is used in the following claims to designate an alloy of the kind described in the above description.

The invention is also capable of other modiflcations and embodiments, and its scope is not limited except by the termsbf the following claims.

What is claimed is:

1. The method of producing a vibratory device which comprises reducing an aluminum base alloy to sheet form, heat-treating the alloy at a temperature above 900 F. for about 30 to 45 minutes, quenching the alloy, maintaining the alloy at a temperature of about 212-F. for about 40 hours, and forming the resulting product.

2. The method of producing a vibratory device which comprises reducing an aluminum base alloy comprising approximately 4% copper, aluminum, and small amounts of silicon, magnesium, manganese and iron to sheet form, heattreating the alloy at a temperature of the order of 900 F. for about 30 to 45 minutes,'quenching the alloy, seasoning the alloy at a low temperature for an extended period, and forming the resulting product.

3. The method of producing a microphone transmitter diaphragm which comprises reducing to stripform an alloy having substantially the following composition: 3.15% to 4.50% copper, 20% to .50% silicon, .40% to 1.00% magnesium, .40% to 1.00% manganese, balance aluminum, maintaining the strip at a temperature of 930 to 960 F. for 30 to 45 minutes, quenching the hot strip in a quenching liquid, cold-rolling the strip to a thickness of about .0017", seasoning the strip by maintaining its temperature at about 212 F. for about 40 hours, and forming the resulting product into a diaphragm.

4. The method of producing a vibratory ribbon which comprises reducing an aluminum base alloy containing copper to a thin sheet, heat-treating the sheet at a tempera re of the order of 900 F., further reducing th sheet to bring it to final thickness, seasoning the sheet. at a temperature of approximately 212 F. for an extended period, and forming it into a ribbon.

5. The method of producing a vibratory ribbon which comprises reducing to-the form of a thin' sheet an alloy having substantially the following composition: 3.15% to 4.50% copper, .20% to .50%- silicon, .40% to 1.00% magnesium, .40% to 1.00% manganese, balance aluminum, maintaining the sheet at a temperature of 930 for 30 to 45 minutes, further reducing the sheet to bringit to final thickness, seasoning the sheet by maintaining it at a temperature of about 212 

